Análisis y optimización de nuevos sistemas determinísticos y estocásticos en gestión de stocks

En el Capítulo 1 se investiga un nuevo modelo EOQ con demanda dependiente del nivel de stock y coste de almacenamiento no lineal con respecto al tiempo de permanencia de los productos en el inventario y la cantidad de productos almacenados. En este contexto, los problemas de minimización de costes y de maximización de beneficios no necesariamente tienen la misma solución óptima. El problema se ha enfocado desde la perspectiva más completa de maximización de beneficios. En el Capítulo 2 se investiga una extensión del problema del newsboy con pedido de emergencia en el cual la fracción de demanda satisfecha con dicho pedido es una función no creciente con respecto al tamaño de la escasez. La función objetivo no es necesariamente convexa, pero se han demostrado resultados teóricos que ayudan a encontrar la solución del problema en casos concretos y a realizar un análisis de sensibilidad de la política óptima.Departamento de Estadística e Investigación Operativ

Physically and chemically modified starches as texturisers of low-fat milk gels

In reduced fat-milk gels lack of fat globules results in undesirable texture changes. This study evaluates application of chemically modified (E-1412,E-1414,E-1422,E-1442), pregelatinized, and both pregelatinized (PG) and chemically modified (PGE-1414) starches as fat replacers. Skimmed milk was substituted with 2% of each starch. The pH and rheological evolution during the acidification process, viscosity of the stirred gels, texture of the set gels and syneresis of all gels were measured. Skimmed and full-fat milk gels were included as controls. All starches had lower or higher pH values, than skimmed or full fat milk gels during acidification. Gelation time was reduced for all starches compared to the skimmed milk gel. For both stirred and set milk gels, with PG, PGE-1414, E-1422 and E-1442 had viscosity/texture values similar or higher to those found for full fat milk gel. For syneresis, E-1412 had drastically increased values when compared with both controls.  Spanish Ministry of Economy and Competitiveness (Project AGL2014-52928-C2)European Regional Development Fund (FEDER

Multinomial logit estimation of a diameter growth matrix model of two Mediterranean pine species in Spain

Understanding diameter growth of the Mediterranean pine species is fundamental for evaluating and making appropriate strategic decisions in forest management. A matrix diameter growth model for two Mediterranean pine forest ecosystems in Spain has been developed. Methods Multinomial logistic (MNL) regression was employed to estimate the transition probabilities of a matrix growth model. The model combines individual tree and stand attributes and explores the effects of independent variables and their relationships with tree size and the probabilities of stand diameter growth. The aim was to predict growth of individual trees by diameter class for a 5-year period. Results MNL model results for diameter growth gave better predictions for Maritime pine (Pinus pinaster Aiton) than for Scots pine (Pinus sylvestris L.). Stand simulations showed that diameter growth probabilities depended on productivity and stand density. Stand simulations under fixed conditions showed that the probabilities of diameter growth increased as site productivity increased and decreased with increased stand density index. Conclusions This study demonstrates the usefulness of matrix growth models as tools to predict growth in Mediterranean pine forests. Stand density and site productivity are key factors in explaining Scots pine and Maritime pine forest growth in the study area.Instituto Universitario de Gestión Forestal Sostenibl

Carbon in heartwood, sapwood and bark along stem profile in three Mediterranean Pinus species

Context Understanding biological processes in forests is necessary to orientate ecosystem management towards potential C sequestration. To achieve this, information is required about changes in forest biomass C pools, including the stem components (bark, sapwood and heartwood). Aims This study aimed to determine whether there are differences in C concentration in axial and radial directions within stem biomass in Pinus nigra, Pinus pinaster and Pinus sylvestris. Methods Wood samples from a permanent plantation in northern Spain were examined for C concentration and wood bulk density. Results The results showed that C concentration was higher in heartwood than in sapwood in the three species. Pinus spp. sapwood C concentration increased along the stem, while the C concentration in heartwood tissue showed the opposite behavior. In bark, Pinus pinaster showed a decreasing trend, in contrast to Pinus nigra and Pinus sylvestris, where higher values were found at the base and top of the stem. Finally, wood bulk density decreased in heartwood, sapwood and bark areas when stem height increased. Estimating C content taking into account different anatomical parts and heights is important in considering the specificity of the different parts because of their potential commercial or ecological use in forest ecosystems.Instituto Universitario de Gestión Forestal Sostenibl

Evaluation and validation of forest models: Insight from Mediterranean and scots pine models in Spain

Producción CientíficaForest models predict tree and stand evolution under different scenarios, thereby supporting decision-making in forest management. Models are complex structures composed of sub-models that estimate forest variables at tree and stand levels. Prediction accuracy has generally been evaluated independently of the model. Integrated sub-models make forest models easier to use and provide predictions for growth, survival, ingrowth and many other tree and stand variables with reduced effort. However, while individual submodel validation is widely practiced and normally done by each author individually, joint model validation remains less explored. This study deploys a useful methodology for evaluating and validating models. After comparing observed and predicted data, several case studies were then proposed to improve the accuracy of the joint model. We used the IBERO model, data from the Spanish National Forest Inventory and the SIMANFOR simulator platform. The accuracy of growth submodels was improved by calibrating their equations, though accuracy was not improved in survival and ingrowth submodels.FEDER - Junta de Castilla y León (CLU-2019-01 y CL-EI-2021-05)Project COMFOR-SUDOE: Integrated and intelligent management of complex forests and mixed-species plantations in Southwest Europe (SOE4/PA/E1012)Project SMART: Bosques mixtos : selvicultura, mitigación, adaptación, resiliencia y trade-offs (VA183P20)Project Integrated Forest Management along complexity gradients (IMFLEX) (PID2021-1262750B-C229

Effect of mycoviruses on growth, spore germination and pathogenicity of the fungus Fusarium circinatum

Producción CientíficaAim of the study: To assess the impact on two mycoviruses recently described in F. circinatum mitovirus 1, and 2-2 (FcMV1 and FcMV2-2) on i) mycelial growth, ii) spore germination and iii) relative necrosis. Material and methods: Fourteen monosporic strains of F. circinatum (one of each pair infected with mycoviruses and the other without them) of the pathogen with and without viruses were selected for the assay. The statistical analysis, were a linear mixed model of analysis of variance considering one between-subjects factor (isolate) and one within-subjects factor with four levels (1=without viruses, 2=only virus FcMV1, 3=only virus FcMV2-2 and 4=both viruses). Main results: Colony growth rates of F. circinatum isolates were significantly reduced in presence of mycoviruses (p=0.002). The spore germination was also reduced in the F. circinatum isolates containing mycovirus as compared to mycovirus-free isolates (p<0.001). No significant differences in lesion lengths caused by F. circinatum were found in relation to the presence/absence of mycovirus (p<0.61). Research highlights: Reduction of the percentage of spore germination in the isolates of F. circinatum with mycovirus infections, as compared to free isolates, provides indications of reduction of metabolic activity and plant physiology are discussed. The lack of significant differences found in the length of the lesions caused by F. circinatum with respect to the presence/absence of mycovirus, indicates that further studies with a larger number of variables are required.Ministerio de Economía, Industria y Competitividad (projects AGL2012-39912 and AGL2015- 69370-R)European Cooperation in Science and Technology (COST Action FP1406 PINESTRENGTH)Portuguese Foundation for Science and Technology (grant SFRH/BPD/122928/2016

Long-term implications of traditional forest regulation methods applied to Maritime pine (Pinus pinaster Ait.) forests in central Spain: a century of management plans

Producción CientíficaPinus pinaster stands in the northern Iberian range (Spain) have been under forest management plans for more than a century. The main goals have been sustainable yield and conservation and enhancement of forest conditions. In the study area, forest management plan implementation started to be effective in the late 19th and early 20th centuries and the plans have been evaluated every ten years. In these forests, a permanent forest compartment method has been applied as the management system. Different regeneration methods have been applied (uniform shelterwood and clear cutting in Soria, selective and uniform shelterwood and continuous cover forestry in Teruel). To analyse the evolution of each forest group, five management indicators have been tested in this study: number of merchantable trees, standing volume, resin production, allowable yield, and harvested volume. Forest situation improvement and maintenance of forest integrity are not only a consequence of the actions planed by foresters, they are also influenced by socio-economic transformations that have occurred during the last century such as the weakness of the resin market, decreasing demand for fire wood, restriction of pasture activities, and increasing recreation use.Ministerio de Educación y Ciencia (project AGL-2001-1780)Ministerio de Educación y Ciencia (project AGL2004-07094-C02-02)Ministerio de Educación y Ciencia (project AGL2007-65795-C02-01

Relationship between environmental parameters and Pinus sylvestris L. site index in forest plantations in northern Spain acidic plateau

Producción CientíficaThe assessment of forest productivity at early stages of stand developmentmay help to define the most appropriate silviculture treatment to be appliedfor each stand. Site index (dominant height at a reference age) is a useful toolfor forest productivity estimation. The aim of this study was to develop amodel to predict site index for Scots pine (Pinus sylvestris L.) plantations innorthern Spain acidic plateau by using soil (physical, chemical and biochemi-cal), climatic and physiographic parameters. To meet this objective, data from35 stands classified into three different site quality classes and 63 soil, cli-matic and physiographic parameters were examined in order to develop a dis-criminant model. After selecting 12 discriminant models which were biologi-cally consistent and presented the higher cross-validated rate of correct classi-fication, a model including four parameters (latitude, inorganic Al, porosityand microbial biomass carbon) as predictors was chosen. The discriminantmodel classified 71% of cases correctly and no inferior-quality stands weremisassigned to the highest quality class. Soil and physiographic parametersincluded in the above model are easily obtainable in the field or by simple la-boratory analysis, thus our results can be easily integrated in operationalforestry to determine site qualitMinisterio de Economía, Industria y Competitividad (Project AGL2011-29701-C02-02,AGL2014-51964-C2-1

An inventory system with time-dependent demand and partial backordering under return on inventory investment maximization

Producción CientíficaIn this article, we study an inventory system for items that have a power demand pattern and where shortages are allowed. We suppose that only a fixed proportion of demand during the stock-out period is backordered. The decision variables are the inventory cycle and the ratio between the initial stock and the total quantity demanded throughout the inventory cycle. The objective is to maximize the Return on Inventory Investment (ROII) defined as the ratio of the profit per unit time over the average inventory cost. After analyzing the objective function, the optimal global solutions for all the possible cases of the inventory problem are determined. These optimal policies that maximize the ROII are, in general, different from those that minimize the total inventory cost per unit time. Finally, a numerical sensitivity analysis of the optimal inventory policy with respect to the system input parameters and some useful managerial insights derived from the results are presented.Ministerio de Ciencia, Innovación y Universidades - Fondo Europeo de Desarrollo Regional (project MTM2017-84150-P

Profitability index maximization in an inventory model with a price- and stock-dependent demand rate in a power-form

Producción CientíficaThis paper presents the optimal policy for an inventory model where the demand rate potentially depends on both selling price and stock level. The goal is the maximization of the profitability index, defined as the ratio income/expense. A numerical algorithm is proposed to calculate the optimal selling price. The optimal values for the depletion time, the cycle time, the maximum profitability index, and the lot size are evaluated from the selling price. The solution shows that the inventory must be replenished when the stock is depleted, i.e., the depletion time is always equal to the cycle time. The optimal policy is obtained with a suitable balance between ordering cost and holding cost. A condition that ensures the profitability of the financial investment in the inventory is established from the initial parameters. Profitability thresholds for several parameters, including the scale and the non-centrality parameters, keeping all the others fixed, are evaluated. The model with an isoelastic price-dependent demand is solved as a particular case. In this last model, all the optimal values are given in a closed form, and a sensitivity analysis is performed for several parameters, including the scale parameter. The results are illustrated with numerical examples.Ministerio de Ciencia, Innovación y Universidades y Fondo Europeo de Desarrollo Regional (FEDER) - (project MTM2017-84150-P